For Jimmy Carter, Madison Square Garden is a place for alchemy. This great arena has seen him transformed from humble man of the people to solemn bearer of the world's burdens, from a politician who preferred to be called Jimmy and shunned official ceremony to a leader who flourished the trappings of office and surrounds himself with the strains of authority.

Symbolism always has been a central part of the Carter political story, and this transformation from plain old Jimmy of 1976, dirt farmer in boots and jeans, to President Carter of 1980, august leader in somber business suit, is no accident. It is all part of his political script.

Tonight's finale showed how the Carter campaign apparently intends to present the new Jimmy to the people. For Carter, the question of impact is crucial. In a real sense, his political fortunes are bound up with the perception of him that his image makers began presenting tonight, just as their previous version was instrumental in winning him the presidency.

Exactly four years ago, the new leader of the Democratic Party made his way to the podium to give his acceptance speech. He did it in a way no one before him had -- by entering from state right throught the crowd of delegates on the convention floor and walking through their ranks up to the rostrum. Moments before, the Democrats had witnessed a film that depicted their nominee as a simple, earnest soul who walked the fields, bent down to let the soil slip through his fingers and listened attentively to ordinary folk.

That night he was offering the public a portrait, self-drawn and self-celebrated, of the outsider who came to power by rising from the ranks of the democracy. Coming after the problems of Watergate and the years of the imperial presidency, simplicity was his hallmark, and part of his ticket to power.

His campaign and message were based on that appeal. He was the kind of guy who carried his own suit bag, made his own bed, stopped his inaugural parade and walked his way to the White House, banned the use of limousines and the playing of "Hail to the Chief."

What a difference four years makes.

Tonight in Madison Square Garden the Democrats convened again to end their quadrennial convention, but under completely different circumstances. Gone was the exhilaration of accomplishing something different, the promise of a fresh start, the sure scent of victory. Weary, a bit battered but still whole, and wary about their November election prospects, they gathered to watch their leader give the summons of their campaign.

The Garden went dark as the house lights dimmed. On the screen was a different portrait of James Earl Carter Jr. This time, the qualities of the insider and the special responsibilities of high office were being celebrated.

Across the screens in the hall was the first sight of a rosy dawn in Washington, D.C., with Washington Monument and Capitol standing in austere majesty beyond the Reflecting Pool stretching away from the Lincoln Memorial.

A quote from Harry Truman sets the theme. No one who ever occupied the White House, Harry said, "is ever allowed to forget he's president of the United States." An announcer's voice, appropriately grave, informs the audience that only 39 men have held that seat of power in the nation's 200-year history. Today, he goes on, the entire world is involved with that man, that office, and this government.

That man, of course, is Jimmy Carter.

For the next 18 minutes the Carter image-makers make their case. It is a curious case, and yet apt: the message is deliberately downbeat, and at times even strikes a negative tone.

No president has been entirely beloved in his own time, the viewers are told, after having been given planning shots of some of our heroic leaders cast in bronze -- Washington, Jefferson, Theodore and Franklin Roosevelt, Kennedy. Of Lincoln's Emancipation Proclamation, it is recalled that some savant of the day said that "the cheek of every American must tingle with shame when he reads it." Truman, the film reminds, was denounced for ineptitude; Wilson was called, in another critic's words, "lily-livered." And on and on calling the roll of the great ones, and showing how they, too, were reviled in their times.

The unsubtle point is that Carter is paying the price that every leader finds presented to him. The obloquy he has suffered will pass when history has a more measured look. Thus, at least, the implied appeal.

Why Carter has been in trouble -- why, indeed, he has fallen to the lowest popularity ratings in modern political history -- is not addressed. This, after all, is a propaganda film, not a historical accounting.

The film does try to answer part of the case against him, though.

For nearly all of the four years of his presidency Carter has been accused of being incapable of dealing with the government he heads. He has been the outsider unable to play the insider's games, the primitive innocent being devoured by the wily Washington sharks.

Not so, his strategists say, and they offer a series of Washington political operatives to prove it. House Speaker Thomas P. (Tip) O'Neill Jr. dismisses the idea that Carter has not been able to get his program through Congress. The truth is, Congress has passed 80 percent of his legislative proposals. Other Democrats from Capitol Hill attest to Carter's special qualities. He's a workhorse, not a showhorse, says Arizona Rep. Morris K. Udall. He may speak softly, but he's a tough man, says Hawaii's Sen. Daniel K. Inouye. He appeals to the best instincts in people, not the worst, says House Majority Leader Jim Wright of Texas.

Andrew Young, his former U.N. ambassador, continues the appeal. He does what's right, not what's popular, he says. And, he adds, Carter happens to be the president at a time when there are no easy issues, and no easy solutions.

Once again the heroic presidential statues flit across the screen. The announcer sounds the final note. We're not electing a status in November, we're electing a president to deal with real-life problems.

It is Jimmy Carter's moment. Once again, as they were four years ago, the house lights are turned up, illuminating an arena filled with Democrats. But this time the script is different.

This time the spotlight picks out the president of the United States standing at the podium. And the band is playing "Hail to the Chief."